Bonded tunable VCSEL with bi-directional actuation

ABSTRACT

A MEMS tunable VCSEL includes a membrane device having a mirror and a distal-side electrostatic cavity for displacing the mirror to increase a size of an optical cavity. A VCSEL device includes an active region for amplifying light. Then, a proximal-side electrostatic cavity is defined between the VCSEL device and the membrane device is used to displace the mirror to decrease a size of an optical cavity.

RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(e) of U.S.Provisional Application No. 62/755,796, filed on Nov. 5, 2018, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Optical coherence analysis relies on the use of the interferencephenomena between a reference wave and an experimental wave or betweentwo parts of an experimental wave to measure distances and thicknesses,and calculate indices of refraction of a sample. Optical CoherenceTomography (OCT) is one example technology that is used to performhigh-resolution cross sectional imaging. It is often applied to imagingbiological tissue structures, for example, on microscopic scales in realtime. Optical waves are reflected from an object or sample and acomputer produces images of cross sections or three-dimensional volumerenderings of the sample by using information on how the waves arechanged upon reflection.

There are a number of different classes of OCT, but Fourier domain OCTcurrently offers the best performance for many applications. Moreover,of the Fourier domain approaches, swept-source OCT has distinctadvantages over techniques such as spectrum-encoded OCT because it iscompatible with balanced and polarization diversity detection. It alsohas advantages for imaging in wavelength regions where inexpensive andfast detector arrays, which are typically required for spectrum-encodedOCT, are not available.

In swept source OCT, the spectral components are not encoded by spatialseparation, but they are encoded in time. The spectrum is eitherfiltered or generated in successive optical frequency sampling intervalsand reconstructed before Fourier-transformation. Using the frequencyscanning swept source, the optical configuration becomes less complexbut the critical performance characteristics now reside in the sourceand especially its frequency sweep rate and tuning accuracy.

High speed frequency tuning, or high sweep rates, for OCT swept sourcesis especially relevant to in-vivo imaging where fast imaging reducesmotion-induced artifacts and reduces the length of the patientprocedure. It can also be used to improve resolution.

Historically, microelectromechanical systems (MEMS)-tunablevertical-cavity surface-emitting lasers (VCSELs) have been used intelecommunications applications. Their tunability enabled a single laserto cover multiple channels of the ITU wavelength division multiplexinggrid.

More recently, these MEMS tunable VCSELs have been proposed as the sweptsources in swept source OCT systems. Here, they have a number ofadvantages. Their short optical cavity lengths combined with the lowmass of their deflectable MEMS membrane mirrors enable high sweepspeeds. Moreover, they are capable of single longitudinal mode operationand are not necessarily subject to mode hopping noise. Thesecharacteristics also contribute to long coherence lengths for deepimaging.

In one example, a MEMS tunable VCSEL, uses a VCSEL, chip or device withan indium phosphide (InP)-based quantum-well active region with agallium arsenide (GaAs)-based oxidized mirror. An electrostaticallyactuated dielectric mirror is suspended over the active region andseparated by an air gap that forms part of the electrostatic cavity forthe dielectric mirror. This electrostatically actuated mirror ismonolithically fabricated on top of the VCSEL, device. The MEMS VCSEL isthen optically pumped by a 980 nanometer (nm) laser, for example.

Monolithically forming the MEMS dielectric mirror on the VCSEL creates anumber of disadvantages, however. First, any processes required to formMEMS mirror must be compatible with the chemistry of the VCSEL.Moreover, the complex fabrication sequence impacts manufacturing yields.

Another class of MEMS tunable VCSELs relies on bonding a MEMS mirrordevice to a VCSEL device. This allows for a separate electrostaticcavity, that is outside the laser's optical resonant cavity. Moreover,the use of this cavity configuration allows the MEMS mirror to be tunedby pulling the mirror away from the active region and the surface of theVCSEL, device. This reduces the risk of snap down. Moreover, since theMEMS mirror device is now bonded to the VCSEL device, much widerlatitude is available in the technologies that are used to fabricate theMEMS mirror device.

SUMMARY OF THE INVENTION

The present invention concerns MEMS tunable VCSELs. Different from priortunable VCSELs, however, the mirror can be pulled in the direction ofthe VCSEL device or pulled away from that device. Moreover, in some ofthe embodiments and/or modes of operation, the mirror can be pulled ineither direction in a dynamic fashion. In other cases, it might bepulled to an initial position and then pulled further in that directionor pulled in the other direction.

In general, according to one aspect, the invention features a MEMStunable VCSEL. It comprises a membrane device having mirror and adistal-side electrostatic cavity for displacing the mirror to increase asize of an optical cavity. A VCSEL device includes an active region foramplifying light. Then, a proximal-side electrostatic cavity is definedbetween the VCSEL device and the membrane device for displacing themirror to decrease a size of an optical cavity.

In general, according to another aspect, the invention features atunable vertical cavity surface emitting laser (VCSEL). It comprises aVCSEL device including an active region for amplifying light and amembrane device, bonded to the VCSEL device, having mirror and adistal-side electrostatic cavity for displacing the mirror to increase asize of an optical cavity. A proximal-side electrostatic cavity isdefined between the VCSEL device and the membrane device for displacingthe mirror to decrease a size of the optical cavity.

In embodiments, the membrane device is metal bonded to the VCSEL. Also,the proximal-side electrostatic cavity can be defined between a membranestructure of the membrane device and a proximal-side electrostaticcavity electrode metal layer on the VCSEL device. Further, a wire bondpad on the membrane device might be electrically connected to theproximal-side electrostatic cavity electrode metal layer.

Further, the membrane structure can be doped for increased conductivity.

Preferably, the VCSEL is protected against damage due to electricaloverstress of the proximal-side electrostatic cavity by ensuring thatthe gap in the electrostatic cavity is prevented from going to 0 by useof an insulating stand-off. This insulating stand off can be the highreflective dielectric coating.

Preferably, a distal-side electrostatic cavity driver is used to apply avoltage to the membrane device, and a proximal-side electrostatic cavitydriver is used to apply a voltage to the VCSEL device.

There can be wire bond pads on the membrane device to which thedistal-side electrostatic cavity driver and the distal-sideelectrostatic cavity driver connect.

In general, according to another aspect, the invention features methodof operation of a tunable vertical cavity surface emitting laser(VCSEL). This method comprises amplifying light in an active region of aVCSEL device, defining an optical cavity for the light between a mirrorlayer of the VCSEL device and a mirror of a membrane device, using adistal-side electrostatic cavity to displace the mirror to increase asize of the optical cavity, and using a proximal-side electrostaticcavity to displace the mirror to decrease a size of the optical cavityusing a proximal-side electrostatic cavity.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 is an exploded perspective view of a MEMS tunable VCSEL,according to the present invention;

FIG. 2 is a front plan view showing the MEMS tunable VCSEL with theVCSEL device shown in phantom;

FIG. 3 is a side plan view showing the MEMS tunable VCSEL, with the MEMSmirror device's optical port shown in phantom;

FIG. 4 is a front plan view showing the MEMS tunable VCSEL;

FIG. 5 is a cross-section taken along line A-A of FIG. 4;

FIG. 6 is a detailed cross-section taken along line B-B of FIG. 4; and

FIG. 7 is a plan view showing the VCSEL device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Further, the singular formsand the articles “a”, “an” and “the” are intended to include the pluralforms as well, unless expressly stated otherwise. It will be furtherunderstood that the terms: includes, comprises, including and/orcomprising, when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. Further, it will be understood that when anelement, including component or subsystem, is referred to and/or shownas being connected or coupled to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent.

Unless otherwise defined, all terms (including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs. It will befurther understood that terms; such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 shows a MEMS tunable VCSEL 100 comprising a MEMS membrane(mirror) device 110 that is bonded to an VCSEL chip or device 112, whichhas been constructed according to the principles of the presentinvention.

In the illustrate design, there is no separate spacer device separatingMEMS mirror device 110 from the VCSEL device 112. The general objectiveis to make the optical cavity of the tunable VCSEL 100 as small aspossible. Thus, in order to control the size of a free space portion ofthe optical cavity, various material layers are deposited on the MEMSmirror device 110 and/or the VCSEL device 112 in order to control thegap. This gap defines the free space portion; which extends between thesurface of the VCSEL device and the surface of the MEMS mirror device.In addition, according to the invention, a proximal-side electrostaticcavity also extends between the MEMS mirror device 110 and/or the VCSELdevice 112.

The optical membrane device 110 comprises handle wafer material 210 thatfunctions as a support. Currently, the handle is made from dopedsilicon, with resistivity <0.1 ohm-cm, carrier concentration >1×10¹⁷cm⁻³, to facilitate electrical contact.

An optical membrane or device layer 212 is added to the handle wafermaterial 210. Typically silicon on isolator (SOI) wafers are used. Themembrane structure 214 is formed in this optical membrane layer 212. Inthe current implementation, the membrane layer 212 is silicon that islow doped with resistivity >1 ohm-cm, carrier concentration <5×10¹⁵cm⁻³, to minimize free carrier absorption of the transmitted light. Forelectrical contact, the membrane layer surface is usually additionallydoped with ion implantation to create a highly doped surface layer(doped usually to >1×10¹⁸ cm⁻³, but at least 1×10¹⁷ cm⁻³ and at least200 Angstroms (Å) thick, usually 500-2000 Å thick). This methodminimizes optical absorption in the membrane layer itself that wouldoccur if the entire layer were highly doped. An insulating (buriedsilicon dioxide) layer 216 separates the optical membrane layer 212 fromthe handle wafer material 210. Typically silicon on isolator (SOI)wafers are used.

During manufacture, the insulating layer 216 functions as asacrificial/release layer, which is partially removed to release themembrane structure 214 from the handle wafer material 210. Then duringoperation, the remaining portions of the insulating layer 216 provideelectrical isolation between the patterned device layer 212 and thehandle material 210.

In the current embodiment, the membrane structure 214 comprises a bodyportion 218. The optical axis of the device 100 passes concentricallythrough this body portion 218 and orthogonal to a plane defined by themembrane layer 212. A diameter of this body portion 218 is preferably300 to 600 micrometers; currently it is about 500 micrometers.

Tethers 220 (four tethers in the illustrated example) defined by arcuateslots 225 fabricated into the device layer 212. The tethers 220 extendradially from the body portion 218 to an outer portion 222, whichcomprises the ring where the tethers 220 terminate. In the currentembodiment, a spiral tether pattern is used.

A membrane mirror dot 250 is disposed on body portion 218 of themembrane structure 214. In some embodiments, the membrane mirror 250 isan optically curved to form an optically concave optical element tothereby form a curved mirror laser cavity. In other cases, the membranemirror 250 is a flat mirror, or even possibly convex.

When a curved membrane mirror 250 is desired, this curvature can becreated by forming a depression in the body portion 218 and thendepositing the material layer or layers that form mirror 250 over thatdepression. In other examples, the membrane mirror 250 can be depositedwith a high amount of compressive material stress that will result inits curvature.

The membrane mirror dot 250 is preferably a reflecting dielectric mirrorstack. In some examples, it is a dichroic mirror-filter that provides adefined reflectivity, such as between 1 and 10%, to the wavelengths oflaser light generated in the laser 100, whereas the optical dot 250 istransmissive to wavelengths of light that are used to optically pump theactive region in the VCSEL device 112. In still other examples, theoptical dot is a reflective metal layer such as aluminum or gold.

In the illustrated embodiment, three metal pads 234 are deposited on theproximal side of the membrane device 110. These are used to solder orthermocompression bond, for example, the VCSEL device 112 onto theproximal face of the membrane device 110. The top pad also provides anelectrical connection to the VCSEL, device 112.

Also provided are three wire bond pads 334A, 334B, and 334C. The leftVCSEL electrode wire bond pad 334A is used to provide an electricalconnection to the metal pads 234. On the other hand, the right membranewire bond pad 334B is used to provide an electrical connection to themembrane layer 212 and thus the membrane structure 214. Finally, thehandle wire bond pad 334C is used to provide an electrical connection tothe handle wafer material 210.

The VCSEL device 112 generally comprises an antireflective coating 114,which is optional, and an active region 118, which preferably has asingle or multiple quantum well structure. The cap layer can be usedbetween the antireflective coating 114, if present, and the activeregion 118. The cap layer protects the active region from thesurface/interface effects at the interface to the AR coating and/or air.The back mirror 116 of the laser cavity is defined by a distributedBragg reflector (DBR) mirror. Finally, a VCSEL, spacer 115, such asGaAS, functions as a substrate and mechanical support.

The material system of the active region 118 of the VCSEL device 112 isselected based on the desired spectral operating range. Common materialsystems are based on III-V semiconductor materials, including binarymaterials, such as GaN, GaAs, InP, GaSb, InAs, as well as ternary,quaternary, and pentenary alloys, such as InGaN, InAlGaN, InGaP, AlGaAs,InGaAs, GaInNAs, GaInNAsSb, AlInGaAs, InGaAsP, AlGaAsSb, AlGaInAsSb,AlAsSb, InGaSb, InAsSb, and InGaAsSb. Collectively, these materialsystems support operating wavelengths from about 400 nanometers (nm) to2000 nm, including longer wavelength ranges extending into multiplemicrometer wavelengths. Semiconductor quantum well and quantum dot gainregions are typically used to obtain especially wide gain and spectralemission bandwidths.

In the preferred embodiment, the polarization of the light generated bythe MEMS tunable VCSEL 100 is preferably controlled and at leaststabilized. In general, this class of devices has a cylindricalresonator that emits linearly polarized light. Typically, the light ispolarized along the crystal directions with one of those directionstypically being stronger than the other. At the same time, the directionof polarization can change with laser current or pumping levels, and thebehaviors often exhibit hysteresis.

Different approaches can be taken to control the polarization. In oneembodiment, polarization selective mirrors are used. In another example,non-cylindrical resonators are used. In still a further embodiment,asymmetrical current injection is used when electrical pumping isemployed. In still other examples, the active region substrate includestrenches or materials layers, which result in an asymmetric stress,strain, heat flux or optical energy distribution, are used in order tostabilize the polarization along a specified stable polarization axis.In still a further example, asymmetric mechanical stress is applied tothe VCSEL device 112 as described in “Tunable VCSEL polarization controlthrough dissimilar die bonding” by Bartley C. Johnson, et al. U.S.patent application Ser. No. 16/409,295, filed on May 10, 2019, which isincorporated herein by this reference, hereinafter Johnson.

Defining the other end of the laser cavity is the rear mirror 116 thatis formed in the VCSEL device 112. In one example, this is a layeradjacent to the active region 116 that creates the refractive indexdiscontinuity that provides for a portion of the light to be reflectedback into the cavity, such as between one and 10%. In other examples,the rear mirror 116 is a high reflecting layer that reflects over 90% ofthe light back into the laser cavity.

In still other examples, the rear VCSEL distributed Bragg reflector(DBR) mirror 116 is a dichroic mirror-filter that provides a definedreflectivity, such as between 1 and 100%, to the wavelengths of laserlight generated in the laser 100, whereas the rear mirror 116 istransmissive to wavelengths of light that are used to optically pump theactive region in the VCSEL, device 112, thus allowing the VCSEL device112 to function as an input port of pump light.

FIG. 2 is front view showing the MEMS tunable VCSEL 100 with the VCSEL,device 112 shown in phantom.

Notably, the view shows the arrangement of the VCSEL device bond pads120A-120E that are arrayed in an arc on the proximal side of the VCSELdevice 112 to enable it to be bonded to the bond pads 234 of the opticalmembrane device 110.

FIG. 3 shows the MEMS tunable VCSEL 100 in side cross-section.

An optical port 240 is provided, extending from a distal side of thehandle wafer material 210 to the membrane structure in cases where themirror 250 is used as an output reflector or to provide for monitoring.If the reflector 250 is used as a back reflector, then the port 240 isnot necessary in some cases.

Further, whether or not this optical port 240 is required also dependsupon the transmissivity of the handle wafer material 210 at the opticalwavelengths over which the MEMS tunable VCSEL 100 must operate.Typically, with no port, the handle wafer material 210 along the opticalaxis must be anti-reflection coated (AR) coated if transmission throughthe backside is required for functionality.

FIG. 4 is front view showing the MEMS tunable VCSEL 100 showing sectionlines A-A and B-B.

FIG. 5 schematically shows the MEMS tunable VCSEL 100 in cross-sectionalong A-A to show a proximal-side electrostatic cavity and a distal-sideelectrostatic cavity 224.

The optical port 240 has generally inward sloping sidewalls 244 that endin the port opening 246. As a result, looking through the distal side ofthe handle wafer 210, the body portion 218 of the membrane structure 214is observed. The port is preferably concentric with the membrane mirrordot 250. Further, the backside of the body portion 218 is coated with amembrane backside AR coating 119 in some examples. This AR coating 119is used to facilitate the coupling of pump light into the laser cavityand/or the coupling of laser light out of the cavity. In still otherexamples, it is reflective to pump light to return pump light back intothe laser cavity.

The thickness of insulating layer 216 defines the electrostatic cavitylength of the distal-side electrostatic cavity 224. Presently, theinsulating layer 216 is between 3.0 and 6.0 μm thick. It is a generalrule of thumb, that electrostatic elements can be tuned over no greaterthan one third the distance of the electrostatic cavity. As result, thebody portion 218, and thus the mirror optical coating 230 can bedeflected between 1 and 3 μm in the distal direction (i.e., away fromthe VCSEL device 112), in one embodiment.

Also shown are details concerning how the VCSEL device 112 is bonded tothe membrane device 110. The MEMS device bond pads 234 bond to VCSELproximal-side electrostatic cavity electrode metal 122. These metallayers are electrically isolated. Specifically, the MEMS device bondpads 234 are separated from the membrane layer 212 by MEMS device bondpad isolation oxide 236; the VCSEL proximal-side electrostatic cavityelectrode metal 122 is isolated from the remainder of the VCSEL deviceby the VCSEL isolation oxide layer 128. Neither of the VCSELproximal-side electrostatic cavity electrode metal 122 nor the VCSELisolation oxide layer 128 interfere with the optical operation sincethey do not extend into the region of the free-space portion 252 of thelaser's optical cavity.

The distal-side electrostatic cavity 224 and the proximal-sideelectrostatic cavity 226 are located on either side of the membranestructure 214. Specifically, the distal-side electrostatic cavity 224 iscreated between the handle wafer material 210 and the membrane structure214, which is the suspended portion of the membrane layer 212. A voltagepotential between the handle wafer material 210 and the membrane layer212 will generate an electrostatic attraction between the layers andpull the membrane structure 214 toward the handle wafer material 210. Onthe other hand, the proximal-side electrostatic cavity 226 is createdbetween the membrane structure 214 and the VCSEL proximal-sideelectrostatic cavity electrode metal 122. A voltage potential betweenthe membrane layer 212 and the VCSEL proximal-side electrostatic cavityelectrode metal 122 will generate an electrostatic attraction betweenthe layers and pull the membrane structure 214 toward the VCSEL device112.

In general, the size of the proximal-side electrostatic cavity 226measured along the device' optical axis is defined by the bond metalthickness, thickness of VCSEL proximal-side electrostatic cavityelectrode metal 122 and MEMS device bond pads 234 along with thethicknesses VCSEL isolation oxide layer 128 and MEMS device bond padisolation oxide 236.

The minimum oxide thickness is determined by the required voltageisolation. Oxide break down is nominally 1000V/micrometer. So, for 200Visolation that would be 2000 A, which is preferably doubled for margin.So the thickness of layers of VCSEL isolation oxide layer 128 and MEMSdevice bond pad isolation oxide 236 is greater than 4000 A.

The current metal bond thickness is 6000 A (each layer) with approx.3000 A compression during bonding. Based on this, the minimum size ofthe proximal-side electrostatic cavity 226 is 0.85 micrometers.

At this minimum electrostatic gap point, a zero optical gap results whenthe membrane mirror dot 250 is 1.7 micrometers thick.

To increase the optical gap, the thickness of the VCSEL isolation oxidelayer 128 can be increased without effecting the operation of thecavity.

In one embodiment, the layer thicknesses of VCSEL, antireflectivecoating 114, VCSEL proximal-side electrostatic cavity electrode metal122, MEMS device bond pads 234, and MEMS device bond pad isolation oxide236 and for the HR coating (250) are such that, under conditions ofelectrical overstress as the deflectable membrane structure (214) ispulled towards the VCSEL device (112), the surface of the membranemirror dot 250 will touch the surface of the VCSEL device 112 before themembrane structure 214 can come into contact with the VCSEL proximalside electrode metal 122. The contact of the membrane to the highlyconductive VCSEL electrode metal can cause permanent electrical damageto the device, whereas the membrane mirror dot 250 is an insulator. Thisfeature protects the device against damage from such electricaloverstress.

On the other hand, isolation oxide layer 128 is not necessary. In fact,if the VCSEL device is not isolated then the active area is also chargedthe same as the metal electrode. Since the HR coating 250 stack is adielectric, the equivalent to an air gap from the membrane to the VCSELis less. This appears to give a significant kick in electrostatic forceas the membrane and HR stack is pulled in.

FIG. 6 is a cross-section along B-B and shows a portion of the membranedevice 110 in the region of the handle wire bond pad 334C.

The handle wire bond pad 334C is fabricated by forming a hole 345through the membrane layer 112 and another hole 342 through the buriedoxide insulating layer 216. This exposes the handle wafer material 210,on which the handle wire bond pad 334C is deposited.

FIG. 7 shows the metal pattern on the proximal side of the VCSEL device112.

In some examples, only 4 pads are used however. The top pad 120C iseliminated to provide a preferential stress direction for polarizationcontrol as described in Johnson.

The VCSEL proximal-side electrostatic cavity electrode metal 122 coversthe center portion of the proximal side of the VCSEL device 112, but forthe very center, wherein the VCSEL antireflective coating 114 remainsexposed.

The VCSEL proximal-side electrostatic cavity electrode metal 122 iselectrically, connected to VCSEL device bond pads 120B-120D byrespective VCSEL bond pad-electrode bridges 124B-124D.

When assembled, the VCSEL proximal-side electrostatic cavity electrodemetal 122 is electrically connected to the VCSEL electrode wire bondpads 334A by the metal bond between the VCSEL device bond pads 120B,120C, 120D and MEMS device bond pads 234. The MEMS device bond pads 234in turn are electrically connected to the VCSEL proximal-sideelectrostatic cavity electrode metal 122 by the VCSEL bridge metal 340.

Thus, with reference to FIG. 2, a distal-side electrostatic cavitydriver 424 applies a voltage between the handle wafer material 210 viathe handle wire bond pad 334C and the membrane layer 212 via themembrane wire bond pad 334B. A proximal-side electrostatic cavity driver426 applies a voltage between the handle wafer material 210 via thehandle wire bond pad 334C and the VCSEL 112 or specifically the VCSELproximal-side electrostatic cavity electrode metal 122 via the leftVCSEL electrode wire bond pad 334A. In this way, a controller 400controls the proximal-side electrostatic cavity 226 by controlling theproximal-side electrostatic cavity driver 426 to translate the bodyportion 214 of the membrane layer 212 toward the VCSEL device 112, andcontroller 400 controls the distal-side electrostatic cavity 224 bycontrolling distal side electrostatic driver 424 to translate the bodyportion 214 of the membrane layer 212 toward the handle material 210.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A tunable vertical cavity surface emitting laser (VCSEL), comprising: a VCSEL device including an active region for amplifying light; and a membrane device, bonded to the VCSEL, device, having a mirror and a distal-side electrostatic cavity for displacing the mirror to increase a size of an optical cavity; and wherein a proximal-side electrostatic cavity is defined between the VCSEL device and the membrane device for displacing the mirror to decrease a size of the optical cavity.
 2. The VCSEL as claimed in claim 1, wherein the membrane device includes metal bonded to the VCSEL.
 3. The VCSEL as claimed in claim 1, wherein the proximal-side electrostatic cavity is defined between a membrane structure of the membrane device and a proximal-side electrostatic cavity electrode metal layer on the VCSEL device.
 4. The VCSEL as claimed in claim 3, wherein a wire bond pad on the membrane device is electrically connected to the proximal-side electrostatic cavity electrode metal layer.
 5. The VCSEL as claimed in claim 3, wherein the membrane structure is doped for increased conductivity.
 6. The VCSEL as claimed in claim 1, wherein the VCSEL is protected against damage due to electrical overstress of the proximal-side electrostatic cavity by ensuring that a gap in the proximal-side electrostatic cavity is prevented from going to 0 by use of an insulating stand-off.
 7. The VCSEL as claimed in claim 6, wherein the insulating stand-off is a high reflective dielectric coating.
 8. The VCSEL as claimed in claim 1, further comprising a distal-side electrostatic cavity driver for applying a voltage to the membrane device, and a proximal-side electrostatic cavity driver for applying a voltage to the VCSEL device.
 9. The VCSEL as claimed in claim 8, further comprising wire bond pads on the membrane device to which the distal-side electrostatic cavity driver and the proximal-side electrostatic cavity driver connect.
 10. The VCSEL as claimed in claim 1, further comprising using a distal-side electrostatic cavity driver for applying a voltage across the distal-side electrostatic cavity and a proximal-side electrostatic cavity driver for applying a voltage across the proximal-side electrostatic cavity.
 11. A method of operation of a tunable vertical cavity surface emitting laser (VCSEL), the method comprising: amplifying light in an active region of a VCSEL device; defining an optical cavity for the light between a mirror layer of the VCSEL device and a mirror of a membrane device; using a distal-side electrostatic cavity to displace the mirror to increase a size of the optical cavity; and using a proximal-side electrostatic cavity to displace the mirror to decrease a size of the optical cavity.
 12. The method as claimed in claim 11, wherein the membrane device includes metal bonded to the VCSEL.
 13. The method as claimed in claim 11, wherein the proximal-side electrostatic cavity is defined between a membrane structure of the membrane device and the VCSEL device.
 14. The method as claimed in claim 13, further comprising electrically connecting to the VCSEL, device by wire bonding to a wire bond pad on the membrane device.
 15. The method as claimed in claim 11, wherein the proximal-side electrostatic cavity is defined between a membrane structure of the membrane device and a proximal-side electrostatic cavity electrode metal layer on the VCSEL device.
 16. The method as claimed in claim 13, wherein the membrane structure is doped for increased conductivity.
 17. The method as claimed in claim 11, wherein the VCSEL is protected against damage due to electrical overstress of the proximal-side electrostatic cavity by ensuring that a gap in the proximal-side electrostatic cavity is prevented from going to 0 by use of an insulating stand-off.
 18. The method as claimed in claim 17, wherein the insulating stand-off is a high reflective dielectric coating.
 19. The method as claimed in claim 11, further comprising using a distal-side electrostatic cavity driver for applying a voltage to the membrane device, and a proximal-side electrostatic cavity driver for applying a voltage to the VCSEL device.
 20. The method as claimed in claim 19, further comprising connecting the distal-side electrostatic cavity driver and the proximal-side electrostatic cavity driver to wire bond pads on the membrane device.
 21. The method as claimed in claim 11, further comprising using a distal-side electrostatic cavity driver for applying a voltage across the distal-side electrostatic cavity and a proximal-side electrostatic cavity driver for applying a voltage across the proximal-side electrostatic cavity. 